Supervisory signal for telephone-switchboards.



rrnn STTns CHARLES E. SCRIBNER, OF CHICAGO, ILLINOIS, ASSIGNOR TO WESTERN ELECTRIC COMPANY, OF SAME PLACE.

SUPERVISORY SIGNAL FOR TELEPHONE-SWITCHBOARDS.

SPECIFICATION forming part of Letters Patent No. 669,709, dated March 12, 1901. Application filed November 25, 1895. Serial No. 570,060. (No model.)

all whom it may concern:

Be it known that I, CHARLES E. SCRIBNER, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented a certain new and useful Improvement in Supervisory Signals for Telephone-SWitchboards, (Case No. 411,) of which ihe following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

My invention concerns signals in telephoneswitchboards which are controlled in the use of the substation-telephones and are designed to inform the operator of the busy or idle condition of the station apparatus. It is a device for permitting the separate operation or response of the signals to indicate independen tly the position of the apparatus at each of two united stations.

It has been common heretofore in exchange systems in which the lines are provided with switches at the substations controlling signaling-currents in the line to associate with. the plug-circuit by which lines are united supervisory signals, one for each plug of a pair, responding independently to currents in the different lines, and in order to attain this independence of operation various expedients have been adopted. Those most favored were to include electromagnetic signals directly in the path of the telephonic current or to employ signals in bridges of the plug-circuit, some appliance being interposed permanentlyin each plug-circuit between the signals for permitting the transmission of telephonic currents through the circuit, but preventing the flow in it of continuous currents for working the signals. The former plan obviously increased the impedance of the circuit, while the latter resulted in a loss of energy in the appliance in the plug circuit and the multiplication of apparatus in the switchboard. In automatically-operating signals it is necessary that the subscribers act of bringing his telephone into position for use shall alter the electrical condition of the line to affect the supervisory signal in the switchboard. The alteration commonly consists in closing the normally-broken line-circuit. In the case of two united lines the circuit may be already completed at the calling-station, but broken at the called station, in which case the supervisory signal referring to the called station must indicate the electrical condition of that line alone independently of the closed condition of the other line. In the present invention the signaling instru ments, which may be relays controlling local circuits of subsidiary signals, are placed in bridges or branches of ihe lines and the separation of the circuits through them is eifected temporarily by the manipulation of a key, which interrupts the plug-circuit. This key may be depressed by the operator whenever she desires to ascertain the condition of the apparatus at either station. The two signals or signal-controlling instruments may be placed in bridges of the united line-circuits, together with a source or sources of current, by which they may be excited when thestation telephones are removed from their switches. Ordinarily a current will flow through each of the signals to each of the stations, so that both signals will be excited as long as either telephone is removed from its hook. The attendant may then ascertain whether the telephone at either station is in use by momentarily depressing the beforementioned key to interrupt the plug-circuit between the signals, whereby each signal will be caused to respond only to current over the corresponding line, if such current exist. The return of both telephones to their normal condition will of course be indicated by the effacement of both supervisory signals.

In the process of making connection between lines the operator will need to use the circuit-breaking key in order to determine Whether a subscriber with whose line connection has been made has responded to the first signal, in order that she may send a second signal if he has not responded. The simultaneous display of both signals may be taken as an indication that the subscribers have terminated conversation and that the connection may be removed. In order that the use of this circuit-interrupting key may not interfere with conversation over the circuit, a condenser or an equivalent appliance may be connected with the key in such a way as to close the break in the circuit as to telephonic currents.

Ihave applied my invention to a well-known 5 form of switchboard in which each line is provided with a relay in a bridge or branch-from the line leading to a source of current common to a large number of the lines and with subsidiary line and supervisory signals con- IO trolled by the relay. The circuits are so arranged that the removal of the telephone at a substation will through the agency of the -relay display a line or initial signal. When connection is made with the line, the linesignal is effaced and a supervisory signal is substituted for it, the supervisory signal becoming excited when ther'elay responds to the cessation of current in the line.

Following is a more specific description of the contrivance with reference to the attached drawing.

The drawing represents two telephone-lines terminating in a telephone-switchboard at a central station, a single pair of connectingplugs, with their associated appliances, be-

ing provided in the switchboard.

The apparatus at the substations is of wellknown type and arrangement. A polarized signal-bell a and a condenser a, are included 0 permanently in a bridge 1 of the line-circuit,

and a transmitting-telephone a and receiving-telephone a are contained in a bridge 2, which is normally open at the contacts of a telephone-switch a. The telephones may be provided wit h the usual local circuit and local source of current or may be constructed to operate with current derived from the central station during the use of the instruments, The telephone-line 3 4 extends from this substation apparatus to the central-office switchboard, where it terminates in the two linesprings of an ordinary three-part spring-jack. The third contact or test-ring of the springjack forms the terminal of a local signal-circuitassociated with the telephone-line. A

battery b, common to all the lines of the exchange, is connected in a bridge of each line, each of such bridges also including a signalcontrolling line-relay c and an impedancecoil cl, one on either side of the battery. Thus the bridge of the line from substation A is made up of the extensions of conductors 3 4, leading from the terminals of the spring-jack to the poles of battery b, the extension from conductor 3 including the signal-controlling device or relay 0 and the extension from conductor 4 including the impedance-coild. The impedance coil d is interposed in the circuit to maintain the static balance of the line and to prevent the shunting of telephonic current tion with wire 6 a wire 7 is led to the ring or local contact-piece of the spring-jack 6. Since the only function of the line-relay is to control a local signal-circuit, it may therefore be designated as a signal-controlling instrument, or, more broadly, a signal instru ment.

The two plugs t'and t" are constructed each with three contact portions to register with the three corresponding pieces of the springjack. Those contact-pieces of the two plugs which make connection with the line-contacts of the spring-jacks are united through linkconductors 9 and 10, respectively, which constitute the plug-circuit. These conductors include, as usual, the switch-springs and an- Vils of a calling-key 7a, which when operated connects with the plug 71 a source of signaling-current. The plug-circuit will in practice be equipped with a key for cutting the operators telephone into circuit. The opera-tors telephonic and signaling appliances have not been shown, being familiar to those skilled in the art of telephony. The local contact-pieces Z of the plugs t' and 11 constitute the terminals of two conductors 11 and 12, respectively, which include supervisory lamps m and m and which are led to the 10- cal battery f. It will be observed that when a plug is inserted into a spring-jack a new branch of the local circuit of battery f is formed in parallel with the circuit 6 through line Iamp g, this new branch being through wires 7 and 11, for instance; The line-lamp g and the supervisory lamp on or m are thus brought into parallel branches of a local circuit including the coil h. This coil should be of such resistance that the current through it shall be insufficient to illuminate the lamps when thus placed in parallel, but that when either the branch 7 11 is open and the other closed or when the branch 6 is op'en,the branch 7 11 being closed,the lamp in the closed branch will be lighted.

The present invention consists in a key at, Whose switch-contacts are interposed in the conductor 9 of the plug-circuit; When this key is in its normal position, the conductor 9 is closed through a short circuit between the switch-springs o 0. hen it is thrown into its alternate position, these springs break the short circuit and become connected through a circuit 13, including a condenser 19. This condenser of course interrupts the continuity of the circuit as to continuous currents, but offers no obstruction to the transmission through the circuit of alternating current, such as telephonic current.

The condenser might of course be replaced by any of the other well-known apparatus which exercise the same function or an equivalent one for this purpose, severing the conductor as to unvarying currents, but permitting the propagation through it of undulating or alternating currents. or equivalent device may be used for a considerable number of plug-circuits, since the operator would have the condenser cut into but one plug-circuit at a time.

The same cond enser Obviously the key may be constructed to interrupt both conductors of the plug-circuit, if desired, or to interrupt the conductors without providing any means for avoiding interference with telephonic currents in the circuit. It will also be apparent that in the event of a different arrangement of circuit connections at the stations, whereby the use of the telephone efiected a diiferent change in the condition of the line, the key might be suitably adapted to render the line-circuits momentarily independent of each other to permit the independent response of the supervisory signals.

When the subscriber-at one station-for example, at station A-removes his telephone from its switch-hook, the circuit of batteryb is closed to the branch 2 at the substation, and the current created in this circuit excites the relay 0 and causes it to close the local circuit 5 6. The line-signal g is illuminated and calls the attention of the operator to this initial signal. The operator then inserts plug '5 into the spring-jack e of the calling-line, continuing the line-circuit to the plug-circuit 9 10, and thus to her telephone, and at the same time shunting, and thus extinguishing, the lamp 9 by means of the supervisory signal m and its circuits. Having learned the order, she inserts the plug 1' into the springjack of the required correspondent-say subscriber B-and transmits a call-signal by means of key It. The insertion of plug 1." into this spring-jack completes a metallic telephone-circuit between the two substations. It also brings the conductor 12, including the supervisory signal m, into the local circuit of line to station B. The establishment of a connection from the wire 3 of line to station B through conductor 9 of the plug-circuit to the corresponding wire to station A brings the relay 0 of the former line into parallel with relay 0, the circuit of both being completed at station A. Hence the relay 0 of the called lineis excited and closes its local circuit 6, so that neither its line-signal nor its supervisory signal on is lighted. After the completion of a connection it should be the duty of the operator to ascertain that the correspondents are in conversation-that is, substantially, that the called subscriber has responded and removed his telephone from its switch-hook. It will be seen that the linecircuit is made up of wires 3 4 from station A, conductors 9 and 10 of the plug-circuit, and wires 3 and 4 to station E. This circuit is closed at the station A, but is as yet broken at station B, at the telephone-switch there. It is required that the operator shall determine the open or closed condition of the line at station B in order to ascertain whether the subscriber at that station has responded to the call. This she will do by depressing the plunger of the key it, interrupting the conductor 9, as before described. There will then be no closed circuit through relay 0, ex cept it be to substation B and through the conductor 2 there. Hence if the telephone be in use at that station the relay will remain excited and the supervisory signal m will remain dark. If the telephone at'station be not in use, the relay 0' will lose its current when the key 'ais depressed and will release its armature and open the branch 6 through its linesignal. This movement will divert the entire current in the local circuit through the supervisory signal m, which will therefore be illuminated and will signify the failure of the subscriber at station E to respond. The operator may then transmit the second call'signal or may notify the subscriber at station A that the correspomlent cannot be reached. At the replacement of both telephones on their switch-hooks bot-h line-cir cuits will be interrupted and both relays will become inert. Hence both local circuits 6 will be broken and the supervisory signals m and m will be lighted. This will be observed by the operator as a signal for disconnection. Thus by the use of this invention the operator is furnished with means for supervising connections which she has established, ascertaining at pleasure whether a signaled subscriber has responded or not without interrupting conversation. This may be done while using her telephone for other purposes, so that distinct economy of her time is attained over the former method of bringing her telephone into the plug-circuit to listen for conversation or to ask whether the correspondent had answered the signal. This is accomplished, too, without the objectionable permanent interposition of condensers or repeating-coils in the plug-circuit.

My invention is defined in the following claims:

1. The combination in a telephone-circuit provided with a switch at each of its terminal stations adapted to interrupt the circuit there, of two signaling instruments in different bridges of the line-circuit and sources of current in the bridges, and a switch adapted to open the circuit intermediate of the two signals, whereby the signals may be permitted to act independently to indicate the position of the switches at the stations, as described.

2. The combination with two telephonelines united through a plug-circuit in a telephone-switchboard, and each provided with a switch at its substation controlled in the use of the telephone for interrupting the line during the disuse of the telephone, of two signaling instruments in different bridges of the line-circuit including a source or sources of current, and a key in the plug circuit adapted to break the said circuit intermediate of the two bridges containing the signals, substantially as described.

3. The combination with a telephone-circuit provided at each of its terminal stations with a switch controlling the continuity of the circuit there, of two signals in different bridges of the telephone-circuit together with a source or sources of current, an appliance adapted to permit the propagation through it of telephonic current but to prevent the flow of .unvarying currents, and a key and circuit connections adapted to include the said appliance in the telephone-circuit intermediate of the said bridges, substantially as described.

4:. In combination, two telephone-lines, a switch at each substation thereof operated in the use of the telephone controlling the continuity of the line-circuit, two relays in different bridges of the circuit together with a source or sources of current, a subsidiary signal controlled by each relay, and a key adapted to interrupt the circuitintermediate of the bridges; whereby the relays may be caused to act together or independently as required, substantially as described.

5. The combination with a telephone-circuit closed at one end and having aswitch at a substation adapted to interrupt the circuit, and a signal in apermanent bridge of the circuit together with a source of current, of a switch-key in the telephone-circuit adapted to interrupt said telephone-circuit between the closed end thereof and the 'point of connection of the said bridge therewith, whereby the signal may be caused to indicate the closed or open condition of the telephone-1 circuit at the substation-switch, substantially j as described.

6. The combination with several plug-circuits, each having a supervisory signal associated with each plug, controlled by a device in a bridge of the circuit of the united lines of which the plug-circuit forms a part, a condenser or other appliance open to unvarying currents but capable of transmitting varying currents, and a key in each plug-circuit adapted to interpose the said appliance in the pl ug-circuit,substantially as described.

7. The combination with telephone-lines and link conductors uniting them, of a telephone in a circuit of the line closed for use at one station and a call'bell in a bridge of the line at the other station, and a switch at the latter station for closing the circuit of the line through a low-resistance path, a bridge of the complete circuit from the link conductor and a signal instrument and a source of current in the bridge, and a key adapted to interrupt the link conductor toward the station where the telephone is in circuit; whereby the signal may be caused to indicate the resistance of the circuit at the called station, as described.

In Witness whereof I hereunto subscribe my name this 19th day of October, A. D. 1895.

CHARLES E. SORIBNER.

Witnesses:

ELLA EDLER, MYRTA F. GREEN. 

